What's the best cleat position for mountain biking?

Start with the cleat positioned so the ball of your foot (first metatarsal head) is directly over or slightly behind the pedal axle. This is the standard starting point. From there, small adjustments based on comfort: move the cleat forward if you experience calf cramps, or back if you want more stability and less calf engagement on long climbs. Angle the cleat so your heel doesn't hit the chainstay or crank arm. Most riders find their ideal position within 2-3mm of the starting point. If you have knee pain, consult a bike fitter—cleat angle and fore/aft position significantly affect knee tracking.